linux-kernel - Re: [PATCH v6 2/8] KVM: x86: Add a helper function for CPUID(0xD,n>=1) enumeration

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Date:   Tue, 13 Aug 2019 14:11:22 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com, mst@...hat.com,
        rkrcmar@...hat.com, jmattson@...gle.com
Subject: Re: [PATCH v6 2/8] KVM: x86: Add a helper function for
 CPUID(0xD,n>=1) enumeration

On Mon, Aug 12, 2019 at 03:18:11PM -0700, Sean Christopherson wrote:
> On Thu, Jul 25, 2019 at 11:12:40AM +0800, Yang Weijiang wrote:
> > To make the code look clean, wrap CPUID(0xD,n>=1) enumeration
> > code in a helper function now.
> > 
> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> > ---
> >  arch/x86/kvm/cpuid.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index 4992e7c99588..29cbde7538a3 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -313,6 +313,50 @@ static int __do_cpuid_ent_emulated(struct kvm_cpuid_entry2 *entry,
> >  	return 0;
> >  }
> >  
> > +static inline int __do_cpuid_dx_leaf(struct kvm_cpuid_entry2 *entry, int *nent,
> 
> 'dx' makes me think of the generic reference to RDX vs EDX.  Maybe
> __do_cpuid_0xd_leaf()?
>
OK, will change it.
> > +				     int maxnent, u64 xss_mask, u64 xcr0_mask,
> > +				     u32 eax_mask)
> > +{
> > +	int idx, i;
> > +	u64 mask;
> > +	u64 supported;
> > +
> > +	for (idx = 1, i = 1; idx < 64; ++idx) {
> 
> Rather than loop here, I think it makes sense to loop in the caller to
> make the code consistent with do_cpuid_7_mask() added by commit
> 
>   54d360d41211 ("KVM: cpuid: extract do_cpuid_7_mask and support multiple subleafs")
> 
OK, will follow the patch to modify the helper.

> > +		mask = ((u64)1 << idx);
> > +		if (*nent >= maxnent)
> > +			return -EINVAL;
> > +
> > +		do_cpuid_1_ent(&entry[i], 0xD, idx);
> > +		if (idx == 1) {
> > +			entry[i].eax &= eax_mask;
> > +			cpuid_mask(&entry[i].eax, CPUID_D_1_EAX);
> > +			supported = xcr0_mask | xss_mask;
> > +			entry[i].ebx = 0;
> > +			entry[i].edx = 0;
> > +			entry[i].ecx &= xss_mask;
> > +			if (entry[i].eax & (F(XSAVES) | F(XSAVEC))) {
> > +				entry[i].ebx =
> > +					xstate_required_size(supported,
> > +							     true);
> > +			}
> > +		} else {
> > +			supported = (entry[i].ecx & 1) ? xss_mask :
> > +				     xcr0_mask;
> > +			if (entry[i].eax == 0 || !(supported & mask))
> > +				continue;
> > +			entry[i].ecx &= 1;
> > +			entry[i].edx = 0;
> > +			if (entry[i].ecx)
> > +				entry[i].ebx = 0;
> > +		}
> > +		entry[i].flags |=
> > +			KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
> > +		++*nent;
> > +		++i;
> > +	}
> > +	return 0;
> > +}
> > +
> 
> Extracting code into a helper should be done in the same patch that the
> existing code is replaced with a call to the helper, i.e. the chunk of the
> next patch that invokes the helper should be squashed with this patch.
>
OK, will squash this patch in next release.

> >  static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> >  				 u32 index, int *nent, int maxnent)
> >  {
> > -- 
> > 2.17.2
> >